EchoDrv.WinRT.App.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <TargetFramework>net5.0-windows10.0.19041</TargetFramework>
  </PropertyGroup>

  <PropertyGroup>
    <CsWinRTIncludes>Contoso</CsWinRTIncludes>
    <CsWinRTGeneratedFilesDir>$(OutDir)</CsWinRTGeneratedFilesDir>
    <CsWinRTWindowsMetadata>10.0.19041.0</CsWinRTWindowsMetadata>
    <Nullable>annotations</Nullable>
    <OutputType>Exe</OutputType>
  </PropertyGroup>

  <PropertyGroup>
    <AutoGenerateBindingRedirects>true</AutoGenerateBindingRedirects>
    <GenerateBindingRedirectsOutputType>true</GenerateBindingRedirectsOutputType>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.Windows.SDK.Contracts" Version="10.0.19041.1" />
    <PackageReference Include="Microsoft.Windows.CsWinRT" Version="1.1.0" />
    <PackageReference Include="System.Runtime.InteropServices.WindowsRuntime" Version="4.3.0" />
    <PackageReference Include="System.Runtime.WindowsRuntime" Version="4.7.0" />
  </ItemGroup>

</Project>

Program.cs

using System;
using System.Threading.Tasks;
using Windows.Storage.Streams;
using System.Runtime.InteropServices.WindowsRuntime;


static class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine("Hello WinRT");

        var guid = new Guid("df964c4d-f0e8-400d-8404-6f140c2a392c");

        var deviceSel = Windows.Devices.Custom.CustomDevice.GetDeviceSelector(guid);
        var devices = Windows.Devices.Enumeration.DeviceInformation.FindAllAsync(deviceSel).GetResults();

        var rot13Device = Windows.Devices.Custom.CustomDevice.FromIdAsync(devices[0].Id,
                                                                          Windows.Devices.Custom.DeviceAccessMode.ReadWrite,
                                                                          Windows.Devices.Custom.DeviceSharingMode.Exclusive).GetResults();
        const ushort UNKONWN_DEVICE_TYPE = 0x00000022;
        var ioctl = new Windows.Devices.Custom.IOControlCode(UNKONWN_DEVICE_TYPE, 0x800, Windows.Devices.Custom.IOControlAccessMode.Any, Windows.Devices.Custom.IOControlBufferingMethod.Buffered);


        String input = "abcxyz";

        var dataWriter = new Windows.Storage.Streams.DataWriter();
        dataWriter.WriteBytes(System.Text.Encoding.ASCII.GetBytes(input));

        uint outSize = (uint)input.Length;
        var outBuf = new Windows.Storage.Streams.Buffer(outSize);


        var res = rot13Device.SendIOControlAsync(ioctl, dataWriter.DetachBuffer(), outBuf).GetResults();

        var dataReader = DataReader.FromBuffer(outBuf);

        var str = dataReader.ReadString(outSize);
        Console.WriteLine(str);
    }
}